Electric alternating-current machine.



PATENTED JAN. 9, 1906.

K. A. LINDSTROM. ELECTRIC ALTERNATING CURRENT MACHINE.

APPLICATION FILED JUNE 29, 1905.

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42 I n f\ H n V U U U U Witnesses;

invenkm" Nam/L AMM VIM/24 m UNITED STATES PATENT OFFICE.

ELECTRIC ALTERNATlNG-CURRENT MACHINE.

Specification of Letters Patent.

Patented Jan. 9, 1906.

Application filed June 29, 1905. Serial No. 267,678.

To air/Z7 whom it may concern:

Be it known that I, KARL ARVID LINDsTRoM,

- a subject of the King of Sweden and Norway, and a resident ofVesteras, Sweden, have invented new and useful Improvements in ElectricAlternating-Current Machines, of which the following is a specification.

This invention relates to improvements in electric alternating-currentmachines, (generators, converters, or motors.)

One of the most common grounds for the deviation of the curve of tensionin an alternating current generator from the simple sinus-linee'. 6.,that the curve of tension has so-called overtones is, as well known, thecircumstance that the more or less open slots in the armature in whichthe winding of the latter is placed causes a discontinuity in themagnetic density of the air-gap, the said discontinuity in the relativemovement of the armature and the magnetic field producing a periodicalvariation of the same density, and thus a corresponding variation of theinduced electromotive force.

Trials have been made to obtain a suitable form of the pole-surface, sothat the curve of the magnetic density in the air-gap, apart from theslots, should be of a simple sinus form, but in vain, since on accountof the slots a deviation from the sinus-curve or an overtone in the samehas always resulted. For several important reasons it is, however, inthe most cases desirable to obviate such overtones, and the presentinvention relates to a device for that purpose. If, as heretoforegenerally has been the case, the onehalf-number of the conductors of thearmature,which are connected in series in one and the same circuit, areunder the south poles, simultaneously as the other half-number occupythe same position in relation to the north poles (though with reverseddirection of current) the overtones produced by the slots in the bothhalves add themselves together. In order to obviate the saidinconvenience, the poles of different polarity of the magnetic field areaccording to the present invention arranged in such manner in relationto the halves of the windings of the armature that the overtones inducedin the one half will be practically displaced half a period in relationto the overtones induced in the other half, whereby the said overtoneswill nullify each other, so that the curve of tension will be free fromvariations of the said kind. The simplest way of carrying out theinvention is to place the poles of the magnetic field, and especiallythe pole-shoes or pole-plates of the same, in such manner with respectto theirrelative position that the distance between the middle of apole-plate and the middle of the next poleplate on the one sidepractically becomes so much greater than the distance to the nextpole-plate on the other side as the distance between the middles ofadjacent slots of the armature. Obviously the difference in saiddistance may, though not so preferably, be made equal to three or livetimes said distances, and so on, between the middles of adjacent slotsor holes. The same result may also be obtained by using one and the samepole-pitch and making every other pole so much thinner that thevariations of the strength of the field, and thereby the variations ofthe curve of tension caused by the first-mentioned variations, occurwith aphase difference of practically half a period at the poles ofditi'erentpolarity. Finally, it is possible to effect a nullifying ofthe waves of tension of higher order by giving the poleplates or theslots of the armature-core an oblique direction.

My invention is diagrammatically illus trated in the accompanyingdrawings, in which Figure 1 shows a developed part of an armature,corresponding field-poles, and curves representing the electromotiveforce; and Figs. 2 and 3 show other such curves.

Referring to the drawings, Fig. 1 shows some poles N S and a part of thearmature having the teeth T and the slots T between them. The armatureis provided with six slots for each pole. In two of the said slotssituated in like manner in relation to adjacent poles are shownconductors b and Z), which are series connected in one and the samecircuit. In each of the said conductors is induced an electromotiveforce which would be represented by the curves F and F, respectively,(the fundamental wave,) if the armature had no slots and the conductorsbe placed on the even surface of the armature. On account of the slotsand the discontinuity of the magnetic density of the air-gap caused bythe same an electromotive force of higher order (an overtone) H and H,respectively, is induced, which adds itself to the fundamental wave. Theresulting curve of the electromotive force thus becomes the sum of boththe said curves. (Not shown in Fig. 1.) The said two conductors areunder the influence of poles of difi erent polarity, and on accountthereof the electromotive forces have different signs; but on account ofthe series connection the electromotive forces of the two conductors addthemselves together both with respect to the fundamental waves, theresultant of which may be represented by the curve F in Fig. 2, and theovertones, the resultant of which may be represented by the curve H inFig. 2. If 'now, as an application of my invention, the pole-shoes ofall the poles indicated by N (the north poles) be displaced to the righta distance corresponding to one-quarter of the distance between themiddle points of two adjacent slots and the pole'shoes of all the polesindicated by S (the south pole) be displaced a corresponding distance tothe left, such displacements being indicated by dotted lines in Fig. 1,so that the distance between the middle of a pole-shoe and the middle ofthe next poleshoe on the one side becomes as much smaller than thedistance to the middle of the poleshoe on the other side as the Wholedistance between the middle-points of two adjacent slots, this will havebut little influence on the fundamental waves (F in Fig. 3) of the twoconductors. On the contrary, the overtones will be displaced in relationto each other onehalf of their period and will therefore practicallyfully neutralize each other. The sum of them will be almost like null,as shown by the curve H in Fig. 3. The curve of electromotive forceresulting from the curves F and H will therefore obtain approximatelythe same clean form as the fundamental wave.

Having now described my invention, what I claim is- 1. Analternating-current machine having the armature-winding placed in moreor less open slots in the armature-core, and poles of the magnetic fieldso placed in relation to the two halves of an armature-winding that thewaves of tension of higher order, the socalled overtones, induced bycertain of the poles in the armature-circuit on account of thediscontinuity of the magnetic field caused by the slots of thearmature-core, are displaced practically half a period in relation tothe corresponding overtones induced by the other poles, substantially asand for the purpose set forth.

2. An alternating-current machine having the armature-Winding placed inmore or less open slots in the armature-core, and every other distancebetween the middle lines at the pole-plates of the magnetic field somuch greater than the intermediate distances as the distance between themiddles of adjacent slots in the armature-core, substantially as and forthe purpose set forth.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

KARL ARVID LINDSTROM.

Witnesses:

GERDA LINDKvIs'r, JOHN DELMAR.

